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Investigation Update: Multistate Outbreak of Human E. coli O145 Infections Linked to Shredded Romaine Lettuce from a Single Processing Facility

Updated May 12, 2010

Today's Highlights

  • There are 23 confirmed and 7 probable cases related to this outbreak from MI, NY, OH, and TN.
  • Investigators in NY obtained an E. coli O145 isolate from an unopened bag of romaine lettuce that matches the outbreak strain.
  • A case-control study in MI found a significant association between illness and consumption of romaine lettuce from the same processing facility.

Confirmed cases of E. coli O145 Infection, United States, by statestate map

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Infections with the outbreak strain of E. coli O145, by date of illness onset (n=30 for whom information was reported as of May 11, 2010) epi curve

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Local and state public health officials in Michigan, New York, Ohio, and Tennessee are investigating human illnesses caused by Escherichia coli (E. coli) O145. CDC is supporting these investigations and facilitating regular communication and information sharing between the states and with the U.S. Food and Drug Administration (FDA).

As of May 11, 2010, a total of 23 confirmed and 7 probable cases related to this outbreak have been reported from 4 states since March 1, 2010. The number of ill persons identified in each state with this strain is: MI (10 confirmed and 3 probable), NY (4 confirmed and 3 probable), OH (8 confirmed and 1 probable), and TN (1 confirmed).
Among the confirmed and probable cases with reported dates available, illnesses began between April 10, 2010 and April 26, 2010. Infected individuals range in age from 13 years old to 31 years old and the median age is 19 years. Sixty-six percent of patients are male.

Among the 30 patients with available information, 12 (40%) were hospitalized. Three patients have developed a type of kidney failure known as hemolytic-uremic syndrome, or HUS. No deaths have been reported.

The outbreak can be visually described with a chart showing the number of persons who became ill each day. This chart is called an epidemic curve or epi curve. Of note, it takes an average of 2 to 3 weeks from the time a person becomes ill to the time when the illness is confirmed by laboratory testing and reported. Please see the E. coli Outbreak Investigations: Timeline for Reporting Cases for more details.

The bacteria responsible for this outbreak are referred to as Shiga toxin-producing E. coli, or STEC. STECs have been associated with human illness, including bloody diarrhea and HUS. STEC bacteria are grouped by serogroups (e.g., O157 or O145). The STEC serogroup found most commonly in U.S. patients is E. coli O157. Other E. coli serogroups in the STEC group, including O145, are sometimes called “non-O157 STECs.” Currently, there are limited public health surveillance data on the occurrence of non-O157 STECs, including E. coli O145; therefore, E. coli O145 may go unreported. Because it is more difficult to identify than E. coli O157, many clinical laboratories do not test for non-O157 STEC infection.

Investigators are using pulsed-field gel electrophoresis (PFGE), a type of DNA fingerprint analysis of E. coli bacteria obtained through diagnostic testing to identify cases of illness that might be part of this outbreak. This testing is done in public health laboratories as part of the PulseNet network. Investigators have established a common definition of confirmed and probable cases related to this outbreak.

Confirmed casesare persons with:

(1) E. coli O145 infection, or E. coli infection with O Group pending, AND
(2) an illness onset on or after March 1, 2010, AND
(3) a DNA fingerprint matching the outbreak strain; AND
(4) an epidemiologic link to the outbreak.

Probable cases are persons with an epidemiologic link to the outbreak and

(1) E. coli O145 infection with an illness onset on or after March 1, 2010 regardless of DNA fingerprint pattern, AND/OR
(2) hemolytic-uremic syndrome; AND/OR
(3) a laboratory isolate positive for Shiga toxin 2 [stx2] or isolate positive for Shiga toxin, but toxin type is unknown or pending.

Current Status of the Investigation

Multiple lines of evidence have implicated shredded romaine lettuce from one processing facility as a source of infection in this outbreak. This evidence includes the identification of the outbreak strain of E. coli O145 from an unopened package of shredded romaine lettuce obtained at an institution that received product from the processing facility linked to the outbreak. A case-control study in Michigan found a significant association between illness and consumption of romaine lettuce processed at the same facility that processed lettuce consumed by ill persons in New York, Ohio and Tennessee.

The lettuce processing company has issued a recall of lettuce produced at their facility as a result of the evidence obtained to date.  An additional recall was issued by a separate company that received lettuce from the same farm as the processing company linked to the outbreak.

This investigation is ongoing. At this time, local, state, and federal health officials are involved in many different types of investigative activities, including:

  • Conducting surveillance for additional illnesses that could be related to the outbreak.
  • Conducting epidemiologic studies that includes gathering detailed information from persons who were ill persons (cases) and from healthy persons (controls) about foods recently eaten and other exposures.
  • Gathering and testing food products that are suspected as possible sources of infection to see if they are contaminated with bacteria.
  • Following any epidemiologic leads gathered from interviews with patients, food purchase information, or from patterns of processing, production and/or distribution of suspected products.
  • FDA is working closely with its state partners in the investigations at the food processor and at the farm level to determine where in the distribution chain the point of contamination likely occurred.

Public health and agriculture officials in Michigan, New York, Ohio, and Tennessee, along with CDC and FDA, are actively engaged in this investigation. Updates on the progress of this investigation will be shared as information becomes available.

Clinical Features/Signs and Symptoms

Most people infected with E. coli develop diarrhea (often bloody) and abdominal cramps 2-8 days (average of 3-4 days) after swallowing the organism, but some illnesses last longer and can be more severe. Infection is usually diagnosed by culture of a stool sample. Many clinical laboratories do not test for non-O157 STEC, such as E. coli O145, because identifying it is more difficult than for E. coli O157. Most people recover within a week, but some develop a severe infection.HUS can begin as the diarrhea is improving and can occur in people of any age but is most common in children under 5 years old and the elderly.

General Information

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Page last modified: May 12, 2010
Content source: National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED)

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